Patent Application
20090135366
This invention relates to liquid crystal displays and, in particular, to a display using polymer dispersed liquid crystal (PDLC) and having an electrode that is thermally transferred to the display.
A liquid crystal display is a capacitive structure, having a dielectric (liquid crystal) between two electrodes, at least one of which is transparent. Often both electrodes are transparent and typically are made from indium tin oxide (ITO) sputtered on a transparent substrate, such as a dimensionally stable, transparent sheet of plastic. In order to provide graphics or alpha-numeric information, at least one of the electrodes is patterned. Typically, this includes screen printing a mask and etching the ITO layer. Etching is a chemical process with attendant problems, and cost, of handling and waste treatment.
Even though screen printing is a well developed technology and, therefore, relatively low in cost, there are disadvantages to screen printing. The resolution of screen printing is not as good as desired. For example, printing a fine line gap, e.g. 0.001″ wide, between conductors cannot be done reliably by screen printing adjacent conductors.
There are many uses for liquid crystal displays that require complicated patterns, e.g. instrument panels. Complicated patterns are presently obtained by patterning both the front electrode and the rear electrode of a liquid crystal display and, occasionally, by combining several liquid crystal displays into one display. Such construction is costly, particularly because the patterned electrodes must be properly registered in order to produce the desired display.
Great expense is incurred in developing a prototype panel when a patterned electrode must be changed or adjusted. It is very desirable to be able to produce prototypes, or make small production runs, inexpensively; i.e., comparable in cost with mass produced panels. Material costs and time could be saved with a system that allowed changes to be made simply and immediately. Ideally, a design could be created on a computer and a xerographic print used as the pattern for an electrode.
In the last twenty years, a particular class of materials, known as polymer dispersed liquid crystals (PDLC), has been developed for displays; e.g., see U.S. Pat. No. 4,992,201 (Pearlman). Devices using these materials operate at 60-120 volts peak-to-peak, unlike earlier liquid crystal materials that operated at much lower voltages, and provide contrast without the need for polarizers. Sometimes referred to as “optical shutters,” polymer dispersed liquid crystals have applications outside the realm of displays.
U.S. Pat. No. 6,842,170 (Akins et al.) discloses a liquid crystal display combined with an electroluminescent (EL) backlight and a touchscreen. The liquid crystal display is part of a keypad, containing a mask layer with images of the buttons on a telephone (0-9, * and #) and other control buttons. It is also disclosed that the liquid crystal display and the EL backlight can share a common substrate.
International Publication WO 2005/121878 discloses a liquid crystal display and an EL backlight on the same side of a substrate. Other permutations are known in the art, with devices on opposite sides of a substrate; e.g., see U.S. Pat. Nos. 5,121,234 (Kucera) and 6,441,551 (Abe et al.). Various interlayers or outer layers for affecting optical performance, e.g. color, reflectance, and dispersion, are also known in the art.
EL devices are not the only devices suitable for backlighting liquid crystal displays. Light guides coupled to various light sources are known in the art; e.g. Published application 2006/0254894 (Jung et al.) discloses a light guide edge lit by a light emitting diode and having features in the light guide for scattering light out of the plane of the light guide. A difficulty with the light guide is the inability to change output once the backlight is constructed. For example, a light guide can provide reasonably uniform lighting over an area or use features to extract light for illuminating selected areas aligned with the features. In either case, the result is fixed and change is costly.
The choice of a technology for a particular display is a balance of competing interests, not the least of which is cost. In the case of cellular telephones, the choice is often based on the presumption that the user will be indoors or at least not in direct sunlight when the telephone is used. In other words, the content of the display all but vanishes in bright light because the display relies on luminous backlighting for visibility. Many liquid crystal displays rely on reflective backlighting. Thus, the backlighting increases or decreases with ambient light and the content of the display remains visible. Some displays try for the best of both worlds with a “transflective” layer between a backlight and a liquid crystal module.
It is known in the art to provide a liquid crystal display including PDLC and a reflective rear electrode of aluminum; e.g. see U.S. Pat. No. 6,825,895 (Nakano et al.). It is known in the art to use a plurality of thermal pins in an array for printing; e.g. see U.S. Pat. No. 3,855,448 (Hanagata et al.). It is also known in the art to thermally print electrically conductive carbon black from a ribbon; e.g. see U.S. Pat. No. 4,269,892 (Shattuck et al.).
In view of the foregoing, it is therefore an object of the invention to provide a PDLC light shutter in which one electrode is thermally bonded to the shutter.
Another object of the invention is to provide a PDLC light shutter in which an electrode is thermally bonded to the light shutter.
A further object of the invention is to provide a PDLC light shutter in which a patterned electrode is thermally bonded to the light shutter.
Another object of the invention is to provide a PDLC light shutter in which a patterned electrode can be changed easily for prototype or low volume production.
A further object of the invention is to provide a PDLC light shutter in which an electrode is thermally bonded by toner powder.
Another object of the invention is to provide a PDLC light shutter having an electrode that is patterned directly from a xerographic print.
The foregoing objects are achieved by the invention in which a PDLC light shutter includes a conductive layer that is thermally bonded to the shutter as an electrode. The layer can be patterned to provide light transmission even when the conductive layer is relatively opaque. A patterned electrode can be reconfigured easily for prototype or low volume production yet the method and apparatus are suitable for volume production as well. Toner powder can be used as an adhesive and the conductive layer is patterned directly from a xerographic print.
A more complete understanding of the invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which:
Light shutter 30 include substrate 31, transparent conductor 32, and PDLC layer 33. The light shutter can be deposited by screen printing or other method, such as roll coating. With substrate 31 operating roll to roll and being roll coated and with ribbon 10 operating roll to roll, light shutters can be produced in considerable volume, yet have custom patterns.
Ribbon 20 and light shutter 30 are illustrated in
For transfer, ribbon 60 brought into contact with light shutter 70 and transient heating is effected without pressure by laser 67, which scans the light shutter, preferably in a raster pattern. In
Unless extremely thin, a metallic film is relatively opaque. In many circumstances, this problem can be overcome by including apertures in the metallic film. As illustrated in
The invention thus provides a liquid crystal display in which the an electrode is thermally bonded to the light shutter. A patterned electrode can be changed easily for prototype or low volume production yet the method and apparatus are suitable for volume production as well. Toner powder can be used as an adhesive and the electrode can be patterned directly from a xerographic print. With apertures, an electrode can be the front electrode, the rear electrode, or both electrodes. Information can be displayed by the shape of the pattern on the electrodes of the light shutter or by a separate graphic sheet.
Having thus described the invention, it will be apparent to those of skill in the art that various modifications can be made within the scope of the invention. For example, a hot platen laminator can be used instead of heated rollers when transferring a patterned toner powder. The bond between layers can be enhanced by treating a layer with an adhesion promoter; e.g. applying a thin coating of solvent to the upper surface of PDLC layer 33 rather than using an adhesive layer. Although raster scanning is preferred, other techniques can be used instead; e.g. vector plotting. A light shutter constructed in accordance with the invention, combined with a light source and a graphics layer, provides a low cost display.
